In commercial fishing operations, the method of fishing known as purse seine fishing is an effective and widely used technique. The method is conceptually simple. A seine, or net, is fitted at the top end with buoyant devices (e.g. floats) and at the lower end with weighting devices (e.g. sinkers). As the seine is deployed in a rough circle, the weighted end of the seine submerges to cause the seine to hang essentially vertically in the water. To provide for seine retrieval, a purse line is attached to the weighted end of the seine by a plurality of connectors, known as purse rings. As the purse line is tightened by fishermen on the fishing vessel, the weighted end of the seine is drawn together to enclose fish within the seine. The weighted end, now pursed, is raised and drawn toward the fishing vessel. Simultaneously, support craft retrieve and draw in the buoyed end of the seine. In this way, fish are trapped in the seine as it is retrieved.
During seine retrieval, the purse line, through its interaction with the purse rings, is used to both purse the seine and draw it toward the fishing vessel. As can be easily imagined, the forces which are generated between the purse line and the purse ring during these operations can be very substantial. Indeed, these forces can cause significant frictional erosion and wear on both the purse line and the surface of the purse rings. The eventual results are a complete failure of the purse rings and a fraying of the purse line which causes the purse line to snag on the netting. In either event, the operation is compromised and the purse rings and cables may need to be replaced.
Recent developments in the commercial fishing area have compounded the problem of purse ring and cable wear because many of the now preferred fishing grounds are located in the Western Pacific Ocean. It happens that purse seiner operations in the Western Pacific require deeper deployment of the seines than in other ocean areas because the relatively deeper thermoclines in the Western Pacific often result in deeper schooling of food fish. Consequently, with the deployment of large seines, the forces required to retrieve the seines (e.g. forces between the purse line and the purse rings) are greatly increased. As a further consequence, standard purse rings, such as are used in other oceans of the world, are generally inadequate for use in the Western Pacific.
Some purse rings are known which incorporate rollers to reduce the friction between the purse ring and the purse line. One example of a roller purse ring was disclosed in U.S. Pat. No. 5,287,645, issued to the inventor of the present invention.
Known roller purse rings suffer from several problems in actual operation. First, one category of problem is directly related to the shape of the frame in the known purse rings. It is desirable to deploy the seine by first stringing the purse rings on a cylindrical metal bar or pipe and then rolling the purse rings sequentially off of the bar as the seine is deployed. This helps eliminate tangling of the seine during deployment. The metal bar is strung through the central passageway in the purse ring frame, through which the purse line passes. The weight of the purse ring and attached equipment is borne by the purse line roller rolling along the cylindrical metal bar.
With known roller purse rings, the oblong frame of the purse ring has relatively straight frame members on the sides between the two ends, with the purse ring roller being near one end, and with the bridle line roller, when present, near the opposite end. The relatively straight side members are sometimes tapered inwardly toward each other, from the width of the purse line roller toward the width of the bridle line roller. The width of the larger end of the central passageway on known purse rings, therefore, is essentially the same width as the purse line roller. The size of the roller and the thickness of the frame are substantially dictated by the weight to be carried by the purse ring and the size of the purse line.
Therefore, in known purse rings, the width of the purse line passageway for a purse ring having a given width of roller is so narrow that the maximum size of cylindrical metal rod that can be strung through the purse ring is too small to be practical. In other words, when using the largest diameter metal rod which can fit through the central passageway in a given size of purse ring, the weight of a typical purse seine with all of its purse rings and sinkers is too great for the metal bar to bear. This results in undesirable bending of the metal bar, impairing the deployment of the seine.
In another aspect, the typical shape of the frame of a known purse ring often results in a problem with the time required for the purse line to center on the roller, when the purse line is winched in to the boat. Purse line rollers are typically double tapered rollers, forming a shallow vee where the purse line is supposed to center for most efficient rolling. The problem arises because known purse ring frames are shaped so as to require the use of a wider than necessary roller, with shallower taper angles, which results in more time being required for the purse line to center on the roller, ultimately resulting in increased drag on the purse line.
A second problem which can occur is related indirectly to the shape of the frame of the purse ring. The problem is that in known roller purse rings, the seine material can become wedged or snagged in crevices between the purse ring frame and the ends of the bridle line roller. This problem also results indirectly from the fact that known purse rings have relatively straight frame members running along the sides of the frame. In known two roller purse rings, the straight side members of the frame angle toward each other from the width of the purse line roller toward the bridle line roller, which is usually narrower. This results in the formation of a crevice at each end of the bridle line roller, in which the seine material can become wedged.
A third problem with known roller purse rings is that the bridle line passageway is often so narrow as to restrict the free movement of the bridle line to some degree, resulting in increased wear on the relatively soft bridle lines. Here again, this problem results indirectly from the shape of the frame, in that the straight sides of the known roller purse ring frames are angled together, producing a relatively narrow bridle line passageway, almost in the shape of a vee, which restricts lateral movement of the bridle line unnecessarily.
Finally, a fourth problem with known roller purse rings is that the size of the cable release opening created by releasing of the cable release arm is limited by the beveled projection of a portion of the frame into the cable release opening. This beveled projection is designed to match up with the beveled end of the pivoting member of the cable release arm. The angle of this bevel on known purse rings is typically less than sixty degrees from the axis of the cable release arm, creating a fairly pronounced projection into the cable release opening. This results in a significant reduction in the available size of the opening for inserting or withdrawing the purse line. Such a steep angle on the bevel was thought to be necessary to maintain alignment of the cable release arm with the frame, under stress applied by the purse line on the inside of the cable release arm. This reduction of the size of the cable release opening is particularly important in smaller purse rings.
In light of the foregoing, the present invention recognizes the need to provide a larger central passageway through the purse ring frame, to allow the stringing of a given size of purse ring on a larger diameter metal bar than previously possible. A further object of the present invention is to eliminate crevices between the frame and the ends of the bridle line roller, to prevent seine material from becoming wedged in the crevices. A still further object of the present invention is to provide a wider bridle line passageway on any given size of purse ring, to allow a larger size bridle line to be used. A yet further object of the present invention is to increase the size of the available cable release opening on any given size of purse ring. Another object of the present invention is to provide a purse ring for purse seiner fishing operations which is easy to install and use, relatively easy to manufacture, and comparatively cost-effective.